Method of adjusting a magnetic head



Jan. 31, 1961 J. BOBB 2,969,584

METHOD OF ADJUSTING A MAGNETIC HEAD Original Filed Jan. 14, 1949attorneys Lloyd J. Bobb,

2,969,584 METHOD OF ADJUSTING A MAGNETIC HEAD Glenside, Pa., assignor,by mesne assignments, to Armour Research Foundation of IllinoisInstitute of Technology, a corporation, not for profit, of IllinoisOriginal application Jan. 14, 1949, Ser. No. 70,837, now

Patent No. 2,745,905, dated May'15, 19,56. Divided and this applicationMay 14, 1956, -Ser. No. 584,795

'3 Claims. (Cl; 29-1555) titled Magnetic Head Assembly, which issued May15,

1956, as Patent No. 2,745,905.

I have found that the pole pieces of magnetic beads which scan amagnetic record while in actual physical contact therewith are subject,over a period of time, to considerable wear. As the metal of the polepieces wears away, the magnetic characteristics of the gap undergochanges as compared with the characteristics of a new head, and, if suchwear continues, the characteristics of the gap may change so completelyas to require thesubstitution of anew head for the worn head.

I have also found that in recording or reproducing heads comprisinglaminations which are asymmetrical about even one plane, and whichtherefore necessarily involve the asymmetrical location of the headwindings with respect to atleast one plane, difficulties areoccasionally encountered in balancing the susceptibility of the windingsto the influence of external electromagnetic fields, with the resultthat a hum or noise voltage' representing the unbalance may appear attheterminals of the head and be amplified along with the signal beingreproduced. The same condition can lead to the'recording of hum andrelated'disturbances when such-a head is being used for recording.

Beyond the foregoing, I have found that for optimum operation ofmagnetic recording and reproducingequipment, particularly where magneticrecords recorded on one apparatus are intended to be reproduced byanother Patented Jan. 31, 1961 It is a further object of the inventionto provide a magnetic head which is symmetrical about three planes,

whereby to provide for simplicity of conversion from one flux gap toanother; and, moreover, to provide a magnetic 5 head in which the twoflux gaps both lie in a plane of symapparatus, it is essential toprovide for extremely accurate orientation of the head relative to arecord being scanned thereby, both as regards the alignment of therecording pole pieces with the record track and'with regard to theangular orientation of the head of one machine with the head of anothermachine which'is intended to be used interchangeably with the samerecord or'records. Such accuracy of orientation is most difficult toattain with head assemblies and head mounting structures of the priorart.

It is a general object of the present invention to provide a magnetichead assembly which overcomes one or more of the difficulties outlinedabove. V

It is another object of the invention to provide a magnetic head havingtwo translating flux gaps so arranged that one of the gaps may be usedafter the pole pieces surrounding the other gaphavebecome'so worn as torender it unsatisfactory in recording-reproducing or erasing, and thustoextend the useful lifeof the'head.

metry of the magnetic head whereby to further simplify the adjustment ofthe head from a position in which one gap is operative-to a position inwhich the other gap is operative.

'Beyond'tlie foregoing, the'invention contemplates a symmetricalarrangement of laminations and windings :wherein the effects of externalmagnetic fields may easily be balanced as between the two windings.

The invention also contemplates novel means of secur- "ing a magnetichead'to, a head support in a manner to provide for simplicity ofadjustment of the position of the "head relative to the record beingscanned.

Finally, the invention contemplates a magnetic head structure achievingone or more of the objectives hereinabove recited and further embodyinga core half member so proportioned in plan as to receive a prewound coilassembly and thus obviate the necessity for winding the coil on thelamination.

How these objects and others which'will appear are attained will beapparent upon consideration of the detailed description of the inventionwhich is contained hereinbelow and the drawings, in which:

"Figure l is a vertical sectional view on an enlarged 30 scale throughthe magnetic head assembly of the invention taken as indicated by theline 1- 1- in Figure 2; Figure 2"is a side elevation of the assembly ofFigure- 1;

Figure 3 is a horizontal sectional view taken from below as indicated bythe line 3-3 in Figure 1;

Figure 4 is a' plan view of the bottom of the head assemblytakenas'indicated'by the line 44 in Figure 2; and

Figure 5 is a plan view, on a still larger scale, of a pair of laminarhalf-members in exaggerated spaced-apart relationship.

The magnetic head assembly of the invention comprises lamination halvesA, a pair of identical winding assemblies B, an upper clamp C, a lowerclamp D, a terminal strip E, and a mounting fixture F.

Each laminationhalf A consists of a stack of laminar half members10'whose symmetrical plan form may best be-seen in Figure 5. The numberof such members 10 in a stack depends upon the desired magneticproperties of .the finished head; for example, in the head illustratedin the drawings, which is intended primarily for erasing magneticrecords, I'employ nine members 10 to make up each half of thelamination. In heads which are intended for other functions, either moreor fewer members 10 may be employed.

Each member 10, and accordingly each lamination half A, is characterizedby a pair of end surfaces 11 adapted to define, in cooperation with thecorresponding surfaces of the other laminationhalf, a flux gap 12 ateach end of the lamination. The surfaces 11 lie in the plane of symmetryof the members 10, and, accordingly, the comis uninterrupted from itsintersection with the gap face atone endto its intersection with the gapface at the other end-of the lamination. Ratherfgenerally stated, the

lamination thus formed is roughly elliptical in shape and ischaracterized by a flux gap at each end, lying on the major axis of theellipse. Geometrically speaking, the inner surface 13 may desirably takethe form of an arc of a circle, and the median portion of the outersurface 14 may also be an arc of a circle having the same center as thesurface 13, while the end portions of the surface 14 are defined by arcshaving somewhat smaller radii.

.When a pair of such lamination assemblies are placed in juxtaposition,with their surfaces 11 in spaced apart parallel relationship, the resultis a lamination symmetrical about three axes and provided with a pair ofidentical flux gaps and with a pair of identical coil-supportingportions, each of which is magnetically and physically related to eachflux gap in the same manner.

Each winding assembly B comprises a coil form 15 comprising arectangular body 16 and a pair of end flanges 17. Body 16 isproportioned to receive the thickness of the lamination stack, and itslength and width are sorelated that while it may he slipped over the endof a lamination stack, it will engage the curved coil-supporting portionof the lamination with suitable snugness. According to the invention, acoil 18 is wound on each form 15 prior to assembly on the laminations.

Clamps C and D are generally C-shaped in section, as may best be seenfrom Figure 2, comprising a body 19 and jaws 20 adapted to engage thelaminations near the flux gaps, as may be seen in Figure 3, and arefurther characterized by holes 21 reinforced by flanges 22 and adaptedto receive clamping screws, as will appear, and holes 23 which areadapted to receive mounting screws, as will also appear. Clamps C and Dare identical, with the exception that the apertures 21 in lower clamp Dare tapped to receive the clamping screws above referred to.

Clamps C and D are preferably formed by die-casting from non-magneticmaterial, which may be metallic, i.e., white metal or aluminum; orresinous, for example, phenol formaldehyde.

Terminal strip E, which may-be formed of any convenient dielectricmaterial, is approximately equal in width to clamp C but is appreciablylonger and carries soldering lugs 24 at either end in positions out ofcontact with clamp C. In addition, terminal strip E is pierced by sixholes adapted to be aligned with holes 21 and 23 in clamps C and D.

Mounting fixture F consists of a shouldered shank 25,

accuse to be aligned with holes 23 of clamps C and D and by a"" raisedhump 28 centrally located with respect to holes 27. Hump 28 is formed byinverting plate 26 and striking the plate with a pointed tool to producea dimple 29 (see Figure l) on the lower side and the hump 28 on theupper side.

While the several elements hereinabove described lend themselves toassembly in a number of different ways, I have found that the followingprocedure is most desirable:

The lamination halves A are formed by inserting the desired number oflaminar half members It in a fixture comprising a trough whose innersurface is congruent with the convex outer surface of the half members10. The members 10 are pressed into approximate position with thefingers and axial pressure applied thereto with a clamp. The members 10are then secured to one another in the clamped position by applying asmall amount of solder.

A plurality of lamination halves so formed are then placed side by sidein another fixture comprising a trough similar to the fixture abovementioned but long enough to accommodate several lamination halves andshallow enough to expose the end surfaces 11. The end surfaces 11 arethen polished to provide flat, coplanar gap-defining surfaces byinverting the fixture containing the lamination halves over a plate uponwhich has been spread a quantity of abrasive material. The fixture withthe surfaces 10 against the abrasive carrying plate is then movedrelative reproducing device.

to the plate to accomplish the actual grinding operation.

The actual assembly of the head is carried out with the assistance of athird fixture consisting of a steel block on whose upper surface aremounted a pair of vertical pins adapted to engage a pair of holes 23 inclamps C and D, for example, the two holes 23 at the upper end of Figure3. The assembly is commenced by dropping a bottom clamp D over the pinswith the jaws 20 facing upwardly.

A winding assembly B is now slipped over each of a pair of laminationhalves A, and the lamination halves, each bearing its winding, aredropped into position on the clamp D.

The top clamp C with the jaws 20 facing downwardly is now dropped intoposition with the pins engaging the holes 23, as in the case of clamp D.The terminal panel E is then dropped into position and the clampingscrews 29 are dropped into the holes 21 and started.

A brass shim 30 is then inserted between the opposing faces of thelamination halves at each end of the lamination.

The various parts are now approximately positioned by hand and pressureis then applied to the end of the lamination opposite the end adjacentthe pins, thus pressing the pole pieces between the pins and forcing thelamination halves toward one another.

The coil leads are now soldered to the lugs on the terminal plate.

The head is next transferred to a test stand where it is subjected tothe influence of an extraneous magnetic field of audible frequency, andthe head is connected to a sound The relative positions of the twolamination halves are then adjusted for minimum audible response byshifting one lamination half relative to the other in a direction alongthe major axis of the lamination.

-When this condition has been attained, the clamping means of screws 30which are dropped through holes 23 in clamps C and D and then started inholes 27 in base plate 26.

When the head assembly has been mounted in the magnetic recordingapparatus by means of shank 25 and is ready for final alignment, astandard record is inserted in the machine, the machine is adjusted forreproducing, and screws 30 are tightened or loosened as the case may be,

rocking the head on hump 28 until the maximum signal is obtained. Whenthe longitudinal axis of the tape is perpendicular to the plane of theflux gap, this may most conveniently be done by first rocking the headin the plane of Figure 2 until the maximum signal is picked up from therecord, thus indicating that correct vertical alignment has been made,and then rocking the head in the plane of Figure 1 until maximum highfrequency response is obtained. Since the reproduction of highfrequencies is rather critical with respect to the angular orientationof the head, this operation results in the optimum angular orientationfor reproduction.

According to the procedure outlined above, the adaptability of themagnetic head of the present invention to mass production is thoroughlyexploited and the assembly of the head itself is coordinated with theassembly and alignment of the complete magnetic recording andreproducing apparatus.

The structural characteristics of the head may be summed up by pointingagain to the fact that each of the laminar half members is symmetricaland that the lamination formed by assembling pairs of such-members ischaracterized by a pair of flux gaps lying in a common plane at oppositeends of the lamination, that the lamination is characterized by a planform lending itself to aslaminations are symmetrical, and that thecomplete head assembly, which is also symmetrical in three planes, issecured to the mounting fixture in a manner to provide for universaladjustment of the position of the gap and its angular orientation withina range adequate for aligning the head relative to a standard record.

Thus according to the invention, the completed head is characterized byphysical, magnetic, and electrical symmetry about three 'axes. As aresult of this construction,

the flux gap at either end of the head may be employed.

in recording or reproducing, extending the useful life of the head.

In addition, the symmetrical arrangement of the various parts of thehead reduces the response of the head to extraneous electrostatic andmagnetic fields by virtue of the fact that the voltages induced in onewinding by such fields are opposed to the voltages induced in the otherwinding.

The generally arcuate shape of the core half members permits the use ofprewound coils, with the advantages pointed out in my copendingapplication hereinabove identified. It should be mentioned that whereverherein the core half members are referred to as being arcuate, andwherever the lamination is referred to as being elliptical, these termsare used in a general rather than in a geometrically precise sense, for,as has been pointed out in the detailed description, the preferred formof the invention involves departures from strictly arcuate or strictlyelliptical form.

I claim:

1. In the method of fabricating a magnetic transducer head includingforming tWo coplanar surfaces at the opposite ends of a semi-ellipticallamination blank, mounting a coil on each of two such blanks,juxtaposing said surfaces of one such blank to the correspondingsurfaces of the other such blank to provide a generally ellipticalconfiguration with non-magnetic gaps between the respective juxtaposedsurfaces of said blanks lying on the major axis of the configuration andwith one of the gapsof size to carry out a magnetic transducing functionwith respect to a magnetic record, and securing the blanks in suchjuxtaposed relation, the improvement characterized by subjecting thejuxtaposed blanks to an extraneous magnetic field, sensing theelectrical output from said coils,

and moving one of said blanks relative to the other in the plane of saidsurfaces to a position corresponding to minimum output of said coils dueto said extraneous magnetic field prior to securing of the blank in saidjuxtaposed relation.

2. T he method of aligning a transducer head in magnetic recording andreproducing apparatus which comprises inserting a magnetic record with astandard magnetic recording thereon in the apparatus in contact with thetransducer head and scanning the record with the head, rocking the headin a plane transverse to the record to angularly adjust the position ofthe head, securing the head as against transverse movement in a positionwhere maximum output is observed and thereafter oscillating the head onan axis normal to the plane of the record and securing the head in theposition of oscillation at which maximum high frequency response isobserved.

3. In the method of assembling a magnetic transducer head includingforming two coplanar surfaces at the op posite ends of a laminationblank, mounting a pre-wound coil on each of two such blanks, juxtaposingthe surfaces of one such blank to the corresponding surfaces of anothersuch blank to provide a generally elliptical configuration withnon-magnetic gaps between the respective juxtaposed surfaces of theblanks lying on the major axis of the configuration and the gaps beingof size to carry out a magnetic transducing function with respect to amagnetic record, the improvement characterized by subjecting thejuxtaposed blanks to an extraneous magnetic field, sensing theelectrical output from said coils, moving one of the blanks relative tothe other of said blanks in a direction along said major axis of saidconfiguration to a position correspondnig to minimum output from saidcoils in the presence of said extraneous magnetic field, securing saidblanks in said position, and polishing the ends of the assembledlaminations at at least one end of said configuration.

References Cited in the file of this patent UNITED STATES PATENTS2,530,584 Pontius Nov. 21, 1950 2,535,480 Begun Dec. 26, 1950 2,555,110Bobb May 29, 1951 2,587,097 Berlant Feb. 26, 1952

